JAKARTA -- When Lion Air Flight 610 crashed into the sea on Oct. 29, an international spotlight was cast on a budget carrier that has placed multibillion-dollar aircraft orders but remains little known outside of Southeast Asia and aviation industry circles.

In less than 20 years, Lion has become Indonesia's top aviation group, with its share of scheduled domestic flights exceeding 50% for the first time in 2017, according to the CAPA Centre for Aviation. It has also become the largest airline group in Southeast Asia by fleet size, with 302 aircraft in service as of Aug. 1 -- nearly 100 more than second-ranked AirAsia and its branded airlines, according to CAPA.

Lion is also a major aircraft buyer. An analysis by Airfinance Journal said that Lion had the second-most aircraft on order among Asia-Pacific airlines as of September this year, with 369 planes worth an estimated $24 billion awaiting delivery.

Now, as Indonesian authorities continue to investigate the cause of the crash that killed 189 people, observers are left to piece together an image of the secretive, privately owned airline from scant public information.

Of all the details about the group -- which consists of low-cost carriers Lion Air and Wings Air and full-service airline Batik Air in Indonesia, as well as budget airlines Malindo Air in Malaysia and Thai Lion Air in Thailand -- its origin is the most well-documented.

Lion Air was established by brothers Rusdi and Kusnan Kirana in 1999 shortly after the collapse of Indonesian President Suharto's New Order regime, which ended the state's monopoly over the aviation industry. The airline started operations the next year.

The brothers come from a modest background. Little is known about Kusnan, but Rusdi, now 55, used to work a part-time job as a ticket seller in Jakarta's Soekarno-Hatta Airport when he was a university student. Before Lion Air, the brothers owned and ran a travel agency called Lion Tours.

Under the slogan "We Make People Fly," Lion Group's business took off as Indonesians and other Southeast Asians grew more affluent and started to travel more by air. The group made global headlines in 2011, when it placed the largest order Boeing had ever received, a $21.7 billion deal for 230 planes.

Then-U.S. President Barack Obama was on hand in Bali for the signing ceremony. Lion made a splash again in 2013 with a $24 billion deal with Europe's Airbus for 234 A320s, which was signed at the Elysee Palace in Paris and witnessed by then-French President Francois Hollande.

As the group quickly expanded its fleet and business, Rusdi entered politics. He was appointed deputy chairman of the National Awakening Party, a member of the ruling coalition, in 2014 and then became an adviser to President Joko Widodo. Earlier this year, he left the job to become Indonesia's ambassador to Malaysia.

According to a 2010 document from Indonesia's Commission for the Supervisory of Business Competition, Rusdi held 45% of PT Lion Mentari Airlines, the Lion Air operator, while Kusnan held the rest. The ownership ratios are believed to still be the same. Rusdi and Kusnan each owned 50% of Wings Abadi Airlines, the operator of Wings Air.

The Kirana brothers were ranked 33rd on the Forbes list of the 50 richest Indonesians last year, with a combined net worth of $970 million, although their wealth declined to $520 million in the U.S. magazine's latest estimate, owing partly to a fall in the Indonesian rupiah.

Low fares have fueled Lion Group's rise to industry leader. It has become the go-to airline group for low- and middle-income Indonesians by offering frequent discounts, making it more price competitive than many budget airlines in the region.

But the rapid expansion of both its business and fleet may have come at a cost. Local media have reported that the group lost money in 2016 and 2017.

"Historically speaking, safety at an airline is most at risk when it is rapidly expanding," said Ryu Tanji, professor at Japan's J.F. Oberlin University and an aviation industry expert. "It becomes very difficult to maintain a proper corporate structure and system, which leads to lower safety."

The Oct. 29 crash was the first fatal accident for Lion Air since a failed landing in 2004 in Solo, a city in Central Java Province, which claimed 25 lives. But it had a spotty safety record in between, with a number of minor incidents as well as runway overruns. The most high-profile of these incidents was in 2013, when a flight to Bali carrying 108 people crashed into the water short of the runway at the island's international airport, although no one was killed.

Lion Air was involved in another accident on Nov. 7, when a flight bound for Jakarta from Fatmawati Soekarno Airport in Bengkulu province was canceled after one of the aircraft's wings hit a pole while preparing for takeoff. Pilots working for the airline have also been found in possession of methamphetamine on a number of occasions, and the airline has been notorious for its chronic delays.

In the past few years, the airline had appeared to improve safety standards, judging from the results of audits by international bodies. In 2016, the European aviation authority lifted a flight ban on the airline after nine years. Lion Air passed the Operational Safety Audit, or IOSA, the global industry standard for airline operational safety, in February 2017, and completed the renewal audit this year, according to the International Air Transport Association, the group behind the audit program.

It is still unclear whether Lion Air was at fault for Flight 610's fatal crash. But transparency has always been lacking at Lion Group, with little to no information available on its performance, including its financial condition. Speculation on a possible initial public offering has emerged on more than one occasion in the past few years, only to fade away.

"From what I can gather, Lion Air does rely a lot on leasing," said Michael Allen, Asia finance editor at Airfinance Journal. "Many of its leasing [deals] are structured through its so-called 'captive lessor' Transportation Partners, based in Singapore."

The leasing company was set up by Rusdi in 2011. Lion Group is seen as favoring sale and lease-back arrangements, whereby Lion sells the aircraft to the leasing company and then leases it back from them, taking the planes off its books.

The South China Morning Post reported in 2015 that the leasing company was expecting 201 Boeing B737 Max passenger aircraft and 174 Airbus A320neo jets worth $40 billion in total.

"One advantage Lion gets by using Transportation Partners is that if the lease is structured through Singapore, Lion can get a preferential tax rate under Singapore's aircraft leasing scheme," Allen said.

This program grants a "concessionary tax rate of 8% on income derived from the leasing of aircraft or aircraft engines and qualifying ancillary activities," according to Singapore's Economic Development Board.

"Transportation Partners also leases some Lion-ordered aircraft to third-party carriers that are not related to Lion," according to Allen. "This helps Lion manage the massive amount of aircraft coming into the fleet."

Lion has tapped financing from GE Capital Aviation Services and its subsidiary PK Airfinance. In April, GE Capital Aviation announced it "had concluded a significant aircraft financing transaction" with Lion covering "21 Boeing 737-900ERs currently operated by Lion Air and 30 aircraft on order by Lion Air, including Boeing 737 Max 8s and 9s as well as the Airbus A320/A321neo." Korea Development Bank also took part in the deal.

Export-Import Bank of the United States has also supported Lion's Boeing orders, saying in 2013 that the lender "has approved a final commitment of $1.1 billion" in funding for aircraft purchases provided by Apple Bank for Savings in New York.

These arranges are believed to enable Lion Group to operate a large fleet of aircraft under less financial stress than outright ownership. An industry insider who asked not to be named said that for the various financiers, lending to the leasing company is more preferable than lending to Lion itself because Transportation Partners leases to other companies as well, diversifying the risks.

As the investigation into the crash of Flight 610 continues, Indonesia's Transport Ministry has instructed Lion Air to temporarily relieve five people, including its technical director and the director of maintenance and engineering, of their duties while the probe is ongoing.

Budi Karya Sumadi, the transport minister, stressed that the decision was made "so that they [the airline] can focus on supporting the investigation," but added: "The suspension is a hint, a warning that they have to be responsible for what they've done."

The flight recorder was recovered last Thursday, but authorities will likely need time to understand what befell the aircraft. Officials from Indonesia's National Transportation Safety Committee have said it may take up to a year to determine the cause of the Lion Air crash, although the committee has pointed to erroneous input from a sensor as a possible factor in the disaster.

"The majority of domestic passengers will see Lion Air as one of the few available options for cheap domestic travel in Indonesia," said Michel Brekelmans, managing director at consulting company SCP/Asia.

"This most recent accident will no doubt put some short-term caution into the market but I think, down the line, the majority of passengers in Indonesia will discount the risk of incidents and accidents associated with air travel to a low probability and continue to fly," he said.